During the catastrophic 2010 Gulf of Mexico oil spill, an estimated 600,000 gallons (2,300,000 liters) of sub-sea chemical dispersants were deployed. The long term effects of these dispersants are not known. Attempts were also made to skim oil at the surface, but only small amounts were actually recovered this way. There is an unfilled need for improved techniques to recover oil that has been spilled in the ocean or other bodies of water.
In calm waters, containment booms are relatively effective at containing surface oil. However, the contained oil still must be collected or burned before the oil layer becomes too thick, or before the sea turns rough. Burning the oil has it own environmental repercussions. It would be far preferable to directly collect the oil and remove it from the environment entirely.
If possible, the recovery of spilled oil by mechanical means would almost always be preferable either to dispersing oil in the water column or to burning. Previous methods of mechanical recovery have generally involved booms to concentrate the oil, and skimmers to remove the oil from water. The effectiveness of skimmers can vary widely, depending on the skimmer system used, the thickness of the oil, and environmental conditions. Various methods of oil skimming exist. Most methods rely either on density differences between oil and water, or on the adhesive properties of oil.
One skimmer that was recently tested in the Gulf of Mexico, the “A Whale,” used vented weirs along a 350-yard converted oil tanker to collect 21 million gallons of oil and water daily. The collected water and oil would be separated later. Apart from its relatively poor collection and separation efficiencies, the gargantuan approach represented by the “A Whale” is probably not practical in most circumstances. The “A Whale” might be analogized to a single, gigantic bee trying to collect honey from tens of thousands of flowers distributed over several square miles. It would be much more efficient to deploy hundreds of smaller bees, an armada or network of smaller or medium-sized skimmers.
Another prior approach is to use a centrifugal separator, such as that of Costner Industries, which employs high centrifugal forces to separate lighter oil from denser water. However, the complexity and energy requirements of such an approach are a major concern. Also, scale-up may be difficult.
Most prior approaches have relied upon collecting oil and water mixtures in barges or in large tanks, and then processing the mixtures onshore to separate oil from water. This approach is inherently slow, difficult, and inefficient. What is collected in the ocean by skimmers typically contains 95% or more water, meaning that the vast bulk of the weight is transported back to land “unnecessarily.” Relatively few prior approaches have attempted to perform separations in situ, while the separator is still actively deployed at sea.
Continuous gravity decanters have previously been used to separate liquids, by allowing liquids to settle to different levels within a generally hollow decanter, based upon differences in the densities of the liquids. To the inventor's knowledge, previous continuous gravity decanters have been used only in more-or-less fixed settings—i.e., either on land or affixed to an offshore platform. To the inventor's knowledge, a continuous gravity decanter has never previously been used for in situ separations of oil and water while a separator is actively deployed at sea, on the waves. See, e.g., “Fluid Statics,” University of Texas at Austin ChE 354 slides (date unknown, available at tinyurl.com/3e32cx8); K. Gavhane, Unit Operations-I, Fluid Flow and Mechanical Operations, pp. 7.13-7.15 (2009) (available at tinyurl.com/429mvqc); ACS Separations and Mass Transfer Products, Liquid-Liquid Coalescer Design Manual (date unknown, available at people.clarkson.edu/˜wilcox/Design/coalesc.pdf); and A. Zanker, “Gravity Settlers, Sizing of Decanters,” in J. McKetta (Ed.), Unit Operations Handbook, vol. 2, Mechanical Separation and Materials Handling (1993) pp. 136-137 (available at tinyurl.com/3otb8he).